An interesting article was published today in the Journal of Precision Medicine describing the importance of testing psychiatry patients for mutations in two companion diagnostic biomarkers, CYP2D6 and CYP2C19.
These are indeed important biomarkers for safe administration of antidepressants and other psychiatric drugs, which over 10% of the American population receive. They also happen to be some of the oldest and most well-established companion diagnostic biomarkers out there, so it seems surprising that there would be a need to encourage their testing.
The very first blog post that I wrote for Biomarker Trends almost 4 years ago focused on this very topic, and I have written numerous times since then about the need to test for CYP2D6 and CYP2C19. These biomarkers are described in far and away the largest number of drug labels of any other companion diagnostic biomarkers, and the majority of these label indications are for psychiatric drugs. (For a detailed breakdown of companion diagnostics, please download our recent free research report: Companion Diagnostic Biomarker Trends)
When I was first examining this topic back in 2012 I was curious about the rate of adoption of CYP2D6 and CYP2C19, and how generally aware psychiatrists were of these biomarkers and the need for testing them. I conducted a simple survey and found that less than 10% of psychiatrists who responded said they test for biomarkers before prescribing drugs to their patients. This wasn’t particularly surprising at the time since laboratory testing isn’t a common practice for psychiatrists.
Since then I have also gained access to reimbursement data from CMS, and was very surprised (and encouraged) to see very significant growth in testing for CYP2D6 and CYP2C19 in recent years. The details about these findings are available here. Progress is certainly being made, but the article mentioned in the beginning of this post makes it clear that more needs to be done.
The stakes are also growing for testing these biomarkers, at least in the case of CYP2C19, as important new associations are being uncovered. In one example, a recent study demonstrated that testing for CYP2C19 significantly reduced the risk of post-operative complications for heart stent patients who were prescribed a particular blood thinner.
If you are involved with testing of these biomarkers, either as a laboratory or a physician, I would be very interested in hearing your thoughts about the rate of testing and factors driving or limiting adoption.